Automatic bus transfer equipment



Aug- 3, 1943- i w. SCHAELCHLIN ET AL 2,326,070

AUTOMATIC BUS TRANSFER EQUIPMENT Filed May 21, 1942 ATTORNEY Patented Aug. 3, 1943k AUTOMATIC BUS TRANSFER EQUIPMENT Walter Sohaelchlin, Forest Hills, Pa., and John C.

iPonstngl, Cleveland, Ohio, assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Penn- Sylvania Application May'21, 1942', Serial No. 443,933

' 4 claims. (o1. 1v1-97) Our invention relates to bus transfer equipment and, more particularly, to automatically operable bus transfer equipment devised for special utility on board naval vessels and other similar fields of application.

On board naval vessels, and some other similar .elds of application, it is extremely important that lighting equipment remain in operation regardless of bomb hits, shell hits, or gunnre of the guns on board ship. To this end, the lighting equipment, and some other electric load units, usually have at least two electricV power sources, a main supply and an emergency supply. The arrangement, therefore, must be such that the two sources of power may be selectively connected to the lighting load. Further, the arrangement must be such that either source can be connected rto the lighting load vautomatically or manually.

In the case of a three-phase alternating-current system, which is generally used, the switching equipment, commonly called a bus transfer, must be capable of detecting phase failures, a reduction in the bus voltage, and a complete failure of the main supply. Il' any one of these faults occurs on the main supply, the bus transfer equipment must be capable of automatically and expeditiously switching the load from the main power supply to' the emergency power supply.

The two vital units of the bus transfer are the switches, or contactors, and the phase failure relay. Ifk the phase failure relay is designed to detect the failure of one phase of the main supply, then a complete voltage failure of the main supply will obviously be detected also.

The bus transfer equipments of the prior art attempt to solve (and to some extent do) the mentioned problemsby utilizing latched-in magnetic contactors and a relatively complicated and expensive phase failure relays. This arrangement is not satisfactory, rst, because of the unreliability due to theV involved interconnections and networks, and, second, because of the large size of the bus transfer equipment. Further, this rather unreliable type of bus transfer equipment is rather expensive.

Certain broad objects of our invention are to provide simple, inexpensive, and reliable bus transfer equipments.

An object'of our invention is the provision of bus transfer equipment that maintains its useful function even when subjected to shocks.

Other objects of our invention will become more apparent from a study of the following specification and drawing, in which:

The single figure is a somewhat diagrammatic showing of our bus transfer equipment.

To illustrate our invention, the showings of the two electric energy generating units, requiring at least two separate generators and two separate prime movers for respectively operating these generators, have not been made because it is thou et that the mere designation el the t ree grot s of buses as Main supply bus, Loail and fency supply bus, respectively, suffices. As part of our bus transfer equipment, we a direct-current relay I. This relay I is with direct current from the threeprase rectifier 2. The drop-out value of this f mcurrent relay can be adjusted much more and reliably than an alternating-current phase failure relay. The adjustment may be cfiected by a suitable design., or selection, of the magnetic circuit of the relay and also by suitable manipulation of the adjustable resistor 3 and by suitable manipulation of the spring tension adjusting il. Further, this directci...,\.ent relay is much cheaper than any of the relays by the prior art.

By the adjustments mentioned, relay I can be caused to pull in and drop out by predetermined Voltage changes of the main supply. If one of the phases on the main supply buses fails, the voltage across coil 5 drops approximately twenty percent. If the effect of coil 5 is adjusted properly, the relay armature will drop out at a twenty percent voltage reduction. This means that this relay will drop out on a failure of any one a complete voltage failure, and when there is a twenty percent or greater reduction in the oltage on the main supply buses. This last advantageous operation is naturally obtained, because the reotiiied voltage on coil 5 will be proportional to the voltage on the three-phase alternating current of the main supply buses.

the main switches for actually transferring the connection, we utilize cam actuated switches, wherein the cams are operated to one position or the other position by electromagnetic means. revision is also made for eeoting such transfer by manually operable means.

A better understandnfr of our invention can probably be had from a study of a typical sequence of operation. If both the main supply and the emergency supply are at normal voltage, and switches E and 'l are closed, all the parts will be in the position shown in the figure.

The load is thus supplied from the main supply. In the event there is on the main supply either a yphase failure, a complete voltage failure, Vor a twenty percent or more voltage reduction, then coil 5 is no longer able to hold the Arelay armature up. The relayV l drops out and Vcontact members B are closed. A circuit is immediatelyV established from bus il, through the normally closed cam operable switch lll, contact members l 8, coil ll of the electromagnetic operatorV l2, through switch to bus l 3. Y

Upon energization of coil H, the armature lil,

through arm le, rotates the camsl, Il, i8 and either maintains or immediately reestablishes the circuits as shown. A Y

This is a very useful feature on board war vessels. For instance, if, by reason of some shock, the cams are caused to rotate out of the position shown, then the electromagnetic device, immediately upon cessation of the first few main vibrations, recloses the circuits as shown.

If Vfor any reason manual control is desired, switches 6 and 'l are opened. This eliminates the control Yeiect of electromagnetic device I2.

From the foregoing, it will be apparent that `we have provided a much simpler, cheaper and a more reliable bus transfer equipment than used by the prior' art. Further, our equipment requires a control panel of only about one third the size ofthe panels used heretofore.

Our specific showing is merely illustrative, and the scope of our invention is naturally broader than the particular circuit arrangement and equipment disclosed. We, therefore, Wish to be limited only by the' scope of the claims hereto three switches'Zil, 25 and 26 will close substanl tially simultaneously that the three switches El',

28 and 2S open. Y This means that now the load buses Vare supplied gency buses. l

The instant rollers til, 3i and 32 have just passed over the humps 33, i and 35. I of these rollers, acting on camsy ll,Y l? andll, respectively, is to aid in completing the counterclockwiserotation. At about the same instant, these rollers Sil-3l and 32 begin to aid with energy from the emerthe counterclockwise rotation, roller 35 is forced down against the spring S'l,y and switch lll is opened, thereby deenergizing coil il. Roller eid-when 4this operation is completed, will hold a position at region 323 on earn i9 corresponding to the position roller 3S is shown Vto hold at region 5G on cam i9,

l It will be noted that when the transfer of the load tothe emergency buses is completed, the

electromagnetic device is again completely doenergized even though this transfer operationcauses the closing of switch di. This will be clear from The force Y appended. 'Y

YWe claim as our invention: i

l. In an electric control for transferring an electricl load circuit from one source of supply to another source of supply, in-ccmbination, a

,three-phase main supply bus, a Vthree-phase emergency supply bus, a three-"phase'load, three spring biased Switches normallybiased to closed position to connect the load to the, main supply, three other spring biasedY Vswitches normally biased to closed position, an electromagnetically operable' cam controller having three cams normally vin position to hold said second three switches open,'a three-phase rectifier connected tothe mainfsupply bus, a relay, having a coil energized through said three-phase rectifier from the main supply and being responsive to drop- Vout in the event of a phase failure, a voltage failure, or a decrease in mainsupply voltage of twenty percent or more, switching means oper- Y able by the dropout of `said relay for energizing the fact that contact members i2 of relay 'l are still open, these contact members having been opened when relay i dropped'out.

' Y As soonas the fault is removed from `the main supply buses, coil 5 again becomes sufficiently energizedto pick up relay l. Contact members E Vius open and contact members l2`close..

The closure or" contact members Il? establishes a clrcuitfrom bus 133 through knife switch l, Contact members e2, coil it of electromagnetic device l2, switch il to bus fl. rl'he electromagnetic device thus operates all the parts to the position shown. The seouc ce is now reversed, namely, first switch. lli opens, then switches 2 28 and 29 close at the same timeswitches 2d, 25 and 2S open, and then switch all opens to again deenergize the electromagnetic device l2.

. If 'the attendant tries to operate the transfer manually, while' the system is capable of automatic transfer of the load say from the main supply to the emergency supply and'again back to the main supply and while knife switches il andl are closed, he will etect a closure of switch di even'before any of the other switches are operated. Coil thus becomes energized. The magnetic devicev i2 thus immediately takes the lcontrol out of the hand of the. attendant and said electromagnetic means for operating the cam controller, whereby said load is disconnected from said main supplyand connected to the emergency supply, and means operablefbyv the controller immediately after the transfer operation for said means. Y Y

2. In an electric bus transfer control for transferring an electri'c'load circuit from one source of supply toy another Ysource of supply, in combination, main alternating-current supply buses, emergency alternating-current Ysupply buses, an electrical load, rectifying means connected Ato said main. alternating-current supply buses, a direct-,current relay connected to be energized from the main sourceofi supply by directeurdeenergizing electromagnetic Vrent through said rectifying means, said relay being so designed and adjusted that it kwill drop out in the event of the occurrence at the main supply cf a phase failure, a complete voltage failure, or a drop in voltage of twenty percent or more, switching means `having two operative positions, Ysaid switching means normallyV being in the position for connecting the loadr to the main Vbuses, Va cutout switch, electromagnetic means energized through said cutout switch: by the dropout of said relay to operate said switching means to disconnect said load from the main buses and to connect said loadV to the emergency buses, means operated by'said switching means, while being operated by said electromagnetic means, for opening said cutout Vswitch to deenergze said electromagnetic means upon the completion of the transfer operation of said switchingmeans.

3. In an electric bus transfer control for transferring an electric load circuit from one source of supply to another source of supply, in combination, main alternating-current supply buses, emergency alternating-current supply buses an electrical load, rectifying means connected to said main alternating-current supply buses, a direct-current relay connected to be energized from the main source of supply by direct current through said rectifying means, said relay being so designed and adjusted that it will drop out in the event of the occurrence at the main supply of a phase failure, a complete voltage failure, or a drop in voltage of twenty percent or more, switching means having two operative positions, said switching means normally being in the position for connecting the load to the main buses, electromagnetic means energized by the dropout of said relay to operate said switching means to disconnect said load from the main buses and to connect said load to the emergency buses.

4. In an electric bus transfer control for transferring an electric load circuit from one source of supply to another source 0f supply, in combination, main alternating-current supply buses, emergency alternating-current supply buses, an

electrical load, rectifying means connect-ed to said main alternating-current supply buses, a direct-current rela-y connected to be energized from the main source of supply by direct current through said rectiiying means, said relay being so designed and adjusted that it will drop out in the event of the occurrence at the main supply of a phase failure, a complete voltage failure, or a drop in voltage of twenty percent or more, switching means having two operative positions, said switching means normally being in the position for connecting the load to the main buses, a cutout switch, electromagnetic means energized through said cutout switch by the dropout of said relay to operate said switching means to disconnect said load from the main buses and to connect said load to the emregency buses, means operated by said switching means, while being operated by said electromagnetic means, for opening said cutout switch to deenergize said electromagnetic means upon the completion of the transfer operation of said switching means, and electromagnetic means energized by the pickup of the relay upon restoration of normal electrical characteristics on the main buses to operate said switching means to transfer the load back to the main buses.

WALTER SCHAELCHLIN. JOI-IN C. PONSTINGL. 

